My interest in HIV-1 began as a child when I volunteered at needle-exchange clinic run by my father. This interest carried forward to my doctoral studies in which I earned a PhD in epidemiology with an emphasis on genetic epidemiology of HIV-1. Since then, I have continued to research the role that host genomic factors play in HIV-1 infection as a Senior Fellow with the International Clinical Research Center at the University of Washington (UW). During both my pre and post-doctoral research, I evaluated the impact of human leukocyte antigen (HLA) class I alleles on multiple HIV-1 outcomes and found several consistent results that I build upon for this K01 Mentored Research Scientist Development Award proposal. First, in a Kenyan perinatal HIV-1 transmission cohort, women who had the A*23 allele had 0.4 log10 copies/mL higher plasma HIV-1 RNA levels and were nearly 3-times as likely to transmit HIV-1 to their infants. Second, among HIV-1 infected individuals from seroidiscordant couples, A*23 was also associated with 0.4 log10 copies/mL higher HIV-1 set-points and B*53 was associated with 0.7 higher set-points. Epidemiologic evidence suggesting that A*23 has a harmful effect during HIV-1 infection is further supported by eight other studies showing that this allele is associated with worse control of HIV-1. However, mechanisms to explain why the A*23 allele is associated with these deleterious outcomes are unknown. Previous studies have demonstrated that certain HLA alleles such as HLA-B*27 and B*57 protect against HIV-1 disease progression by restricting specific CD8+ T-cell epitopes that elicit immune responses of higher magnitude and functionality; mechanisms to explain effects of other alleles on HIV-1 are not yet understood. One hypothesis to explain associations of HLA-A*23 and B*53 with increased HIV-1 set-point is that the harmful effects are elicited in a T-cell epitope dependent manner that results in inefficient cytotoxic T-lymphocyte (CTL) responses in response to HIV-1 infection. To evaluate this hypothesis, we propose to 1) use IFN-? ELISpot assays to determine if CTL responses to specific T-cell epitopes presented by A*23 or B*53 are associated with changes in set-point; and 2) compare qualitative differences in T-cell responses restricted by harmful and protective HLA alleles using intracellular cytokine staining and flow cytometry. Understanding why A*23 is associated with worse control of HIV-1 may help identify immunogens that hinder effectiveness of T-cell based vaccines and may further elucidate functional characteristics that differentiate protective from ineffective CTL. Alternatively, studis have increasingly demonstrated that HLA alleles can also influence immune responsiveness through alternative mechanisms such as binding to to the immunoglobulin-like transcript 4 (ILT4) receptor on dendritic cells (DC). HLA binding to ILT4 can alter DC maturation and development of tolerogenic T-cell responses. Thus, it is possible that the A*23 and B*53 alleles lead to worse control of HIV-1 by binding the ILT4 receptor more strongly than other alleles. Evaluating whether HLA-A*23 and B*53 associate with higher HIV-1 set-point levels via CTL or ILT4 mechanisms is an innovative way to constrast mechanisms for protective and harmful HLA alleles and may elucidate natural pathways leading to protection that could be used in vaccines or therapeutic interventions. Due to the interdisciplinary nature of the research objectives, I have assembled a mentoring team with considerable expertise in HIV-1 epidemiology and global health and HIV-1 immunology. Dr. Jairam Lingappa (Medicine and Global Health, UW) will serve as the primary mentor and will provide daily guidance regarding all aspects of the research and training plan with particular focus on project coordination, data interpretation, and professional development. Dr. Nicole Frahm (Associate Director for Laboratory Science at the HIV Vaccine Trials Network and Assistant Professor of Global Health, UW) will provide mentoring regarding pathobiology and immunology, and will provide laboratory space for conducting assays and experiments. As suggested by the reviewers, I have also assembled an Advisory Committee to provide evaluation and feedback regarding career progression. The Advisory Committee includes Drs. Connie Celum (Professor of Global Health, Medicine, and Epidemiology), Jim Mullins (Professor of Microbiology and Medicine), Julie McElrath (Director, HIV Vaccine Trials Network Laboratory Program) and Peter Gilbert (Co-Director of the Statistical Data Management Center of the HIV Vaccine Trials Network and Research Professor of Biostatistics). In addition to specific mentoring, I will also complete formal coursework covering HIV-1 molecular biology and will participate in conferences and other meetings where I will present my research. Overall, this research and training program will combine my expertise in epidemiology and biostatistics with new experiences working directly with basic science data, positioning me to make useful contributions to HIV- 1 research by applying interdisciplinary approaches and fulfill my short and long-term career objectives of obtaining independent R01 funding and becoming an interdisplinary research faculty member.